will let ya in on a lil trick when ya do a compression test do it once on all cylinders then do it again but ad a few squrts of oil from an oil can then check the compression if the reading goes up its rings and if it stays the same its valves/head gasket

I think the easiest way to determine if it is valve related or piston ring related cylinder pressure loss is to do the compression check again. On the cylinder that is low check the compression, then remove the tester, add some oil into the spark plug hole (not too much!), and retest. If the pressure goes up, the rings are shot. If the pressure stays the same, it is valve/head related. Good luck!

-Andy

Yeah that is the easiest way -- forgot it even though I did the same test last month on a car. If the head gasket is blown, the test won't tell, you might think it's valves and get discouraged. But then you can check adjacent cylinders -- if one is low also chances are it's a blown gasket leaking between the two adjacent cylinders. That still leaves blown gasket leaking into water or oil passages, but that has its own symptoms, like water in the oil, unusual (non-black, non-disappearing) smoke out the tailpipe, or oil in the water. Keep in mind that it's normal for cars when first started, until warmed up a bit, dribble some water out the tailpipe possibly with black soot in it or some water smoke that quickly dissipates into the air. It's the bluish-white smoke that blows away but doesn't evaporate that indicates oil burning from the rings or valve stems.

Going off topic a little, valves are easy to change (don't know about the CA18, but easy on an A12/A14) and head gasket even easier. To replace a burnt valve, usually you can just lap the seat (inexpensive tool is just a suction cup on a stick) with lapping compound, wash the compound off and put the new valve in. Unless you are racing there's often no need to do the 3-angle grinding job again -- the valve burns but the seat usually doesn't, even when the valve is badly burned. To compress the valve sping you can rent a special spring compressor from the rental store.

However if its still running smooth wouldnt that lean more towards the the rings gone. When the valves go doesnt it usually run like ####.

if a valve is gone yes it does run like ####. it also runs like #### if the bolts come loose on the rocker assembly that happened to me it sounds cool though